1. Field of the Invention
The invention relates to color image processing apparatus which corrects a plurality of color components of an input color image signal thereby to derive a corresponding plurality of color image signals for recording, and also to color image forming apparatus which derive color hard copies from the color image signals thus obtained.
2. Description of the Prior Art
Various recording systems are used in digital image recording devices which form color images. Electrophotographic systems form respective color-decomposed potential images in corresponding color plates, develope and transfer them, and superimpose them for three colors (usually cyan, magenta and yellow) or four colors (the above three colors plus black), thereby forming a color image. Ink jet recording systems inject three or four color inks from respective nozzles corresponding to decomposed color image signals, thereby forming a color image. Thermal-sensitive transfer recording systems each perform thermal transfer of respective colors using corresponding thermal heads to form a color image. These systems are the same in that they superimpose four colors using four color (cyan(C), magenta(M), yellow(Y), or black(K)) inks or toners. In this case, since the respective actual spectral reflectance characteristics of color materials, i.e. cyan, magenta and yellow differ from the corresponding ideal ones, color decomposed data are corrected in advance using a method referred to as masking to eliminate unwanted color components mixed additionally at the printing stage in order to realize correct colors. The computation for this masking is usually performed in accordance with the following formula (1): ##EQU1## where C, M, Y denote data on cyan, magenta and yellow before masking and C', M' and Y' denote data on after masking, and .alpha..sub.C -.gamma..sub.Y are correction factors for masking.
In conventional color plate making and printing techniques, information generation does not require supply of a corresponding immediate printing output, so that a computer performs masking in advance. However, recently, various recording systems mentioned above allow information generation to color images to be output immediately, thereby causing hardware to perform high-speed masking. FIG. 6 shows a hardware structure for performing conventional high-speed masking. In FIG. 6, memories called look-up tables (LUTs) 6-1-6-3 store the computation results of the formula (1) therein. When these look-up tables are addressed with respective input color signals C, M and Y, output signals C', M' and Y' are immediately read. When each of input color signals C, M and Y consists of 8 bits, each of output signals C', M' and Y' usually consists of 8 bits. In this case, memory 6-1 is a 8-bit data memory which addressed with 24 bits and hence has a capacity of 16 megabytes. Furthermore, the output includes three colors, and the memory must have an enormous capacity of 48 megabytes in all. Thus the apparatus cost as well as size are increased.